The present invention relates to a device for manufacturing so-called gobs from glass. Such gobs serve as intermediate products for optical articles, such as lenses.
U.S. Pat. No. 5,762,673 describes a device, in which glass balls defined by dropping are produced from a molten mass of glass. The glass balls are kept in suspension in a gas stream while at the same time being brought to a specific temperature and a specific viscosity. In a further procedural step the glass gobs are subjected to a pressing procedure, followed by further processing steps.
The present invention focuses on that phase of the known process, in which the glass gob is kept in suspension for a certain period by means of a gas stream. During this time the glass balls or gobs can cool off, be heated and/or kept at a certain temperature. The associated device comprises a membrane of an open-pored material as an essential element. The membrane may be discoid. The disc can be even or have the shape of a trough corresponding to the shape of the glass gob.
JP-A-H10-139465 describes such membranes. These have the form of a trough-like circular disc which is clamped by its outer circumference in the carrier. The circular disc is relatively thin-walled and comprises an upper and lower surface. A compressed gas is applied to the lower surface, which migrates through the pores of the membrane and exits again at the upper surface of the membrane. Glass drops from a molten mass are applied intermittently to the membrane. The individual glass drop is suspended for a certain time by the compressed gas exiting from the upper membrane surface, as per procedural requirements.
The known devices are encumbered with disadvantages. A particular disadvantage is that the membrane material exhibits minimal stability only. From this viewpoint considerable wall strength of the membrane is preferable to reduce the risk of breakage.
On the other hand, with a given gas pressure, a specific quantity of gas should penetrate through the membrane from top to bottom to guarantee that the gas cushion required to levitate the glass gob develops. To prevent unnecessarily high supply gas pressures, the membrane must be made thin-walled.